Influence of steam sterilization on the mechanical and low-cycle fatigue properties of polyetheretherketone parts obtained by material extrusion additive manufacturing technology

• Steam sterilization must be considered in the qualification of additively manufactured PEEK implants. • Sterilization induces a decoupling between tensile embrittlement and fatigue damage evolution. • Fatigue behavior is governed by altered crack propagation mechanisms rather than static ductility. • The findings support fatigue-oriented design validation of AM polymer components. Steam sterilization is a mandatory post-processing step for polymer-based medical implants; however, its influence on fatigue damage evolution in additively manufactured high-performance polymers remains insufficiently understood. In this study, we investigate how high-temperature steam sterilization (134 °C) alters the mechanical response and low-cycle fatigue behavior of polyetheretherketone (PEEK) components produced by material extrusion (MEX). A combined experimental framework involving quasi-static tensile testing supported by digital image correlation (DIC), strain-controlled low-cycle fatigue experiments, Manson–Coffin–Basquin (MCB) modeling, and post-mortem scanning electron microscopy was employed to compare as-built (BOC) and steam-sterilized (OC) specimens. While steam sterilization induces a reduction in tensile ductility and suppresses macroscopic necking, fatigue experiments reveal a counterintuitive response: sterilized specimens exhibit extended fatigue crack propagation zones and altered damage evolution despite their more brittle-like monotonic behavior. The results demonstrate a non-trivial decoupling between monotonic tensile embrittlement and fatigue crack propagation mechanisms in MEX-processed PEEK. Fractographic and hysteresis analyses indicate that sterilization modifies inter-filament cohesion and volumetric damage mechanisms, promoting stable fatigue crack growth at lower effective stress intensities rather than premature catastrophic failure. These findings provide mechanistic insight into sterilization-induced fatigue degradation pathways in additively manufactured PEEK and highlight the necessity of considering post-processing effects beyond static properties when qualifying polymer implants for fatigue-sensitive biomedical applications.